Thermal convection under external modulation of the driving: II experiments.

Experimental data are presented on the temperature response of a Rayleigh-Benard system to sinusoidal modulation of the heat current supplied to the lower plate near the onset of convection. Quantitative results are obtained for the average convective current as a function of the average Rayleigh number and of the amplitude and frequency of the modulation. Results are also presented on the temporal behavior of the response, above the convective threshold. The data are interpreted in terms of a previously proposed model which is a generalization of the Lorenz equations to periodic external driving. An important effect included in the model is the dynamic thermal mismatch between the sidewalls and the fluid which leads to an imperfect bifurcation between the conductive and convective states.